SL vs M SL Tax Code NZ: What’s the Real Difference?

“SL” isn’t a standalone tax code. It is a suffix added to whichever base code already applies to you, signalling that your employer should also deduct student loan repayments. M SL simply means “main job code, plus student loan.” The same suffix can attach to any code: SB SL, S SL, SH SL, ST SL, or SA SL, depending on your situation.

See exactly how SL affects your take-home pay using our free PAYE Calculator.

This guide provides general information only, not tax advice. Confirm your exact tax code using Inland Revenue’s IR330 form or official tax code finder.

Why “SL vs M SL” Is a Bit of a Trick Question

The comparison implies SL and M SL are two competing options — they’re not. SL never appears alone on a valid tax code for salary and wage earners; it’s always attached to a base code that describes your actual employment situation (main job, secondary job, or benefit income). Asking “SL or M SL?” is a bit like asking “should I choose ‘large’ or ‘large pepperoni pizza’?” — the second option already contains the first, plus one extra piece of information.

What SL actually does, regardless of which base code it’s attached to: it tells your employer or payer to deduct 12% of your income above the $24,128/year repayment threshold, on top of your ordinary PAYE income tax — see our full Student Loan Calculator for the complete repayment mechanics.

Every Base Code + SL Combination

Base code	Meaning	With SL added
M	Main job, no student loan	M SL
ME	Main job, eligible for Independent Earner Tax Credit	ME SL
SB	Secondary job, total income across all jobs under $15,600	SB SL
S	Secondary job, total income $15,601–$53,500	S SL
SH	Secondary job, total income $53,501–$78,100	SH SL
ST	Secondary job, total income $78,101–$180,000	ST SL
SA	Secondary job, total income over $180,000	SA SL

Note on formatting: IRD’s current IR330 form writes these with a space (M SL, ME SL). Some older payslips or payroll systems show a concatenated version instead (ML, MLE) — both mean exactly the same thing.

When to Use M SL Specifically

Use M SL when your student-loan-bearing job is your main or highest-paying source of income, and you don’t separately qualify for the Independent Earner Tax Credit (which would make it ME SL instead). This is by far the most common SL combination, since most people with a student loan have just one job.

When to Use a Secondary Code + SL Instead

If your student loan applies to a second job (not your main one), you need a secondary code with the SL suffix — and critically, which secondary code depends on your combined income across all jobs, not just the second job’s income in isolation.

This is where the single most common tax code mistake happens: using M (instead of a secondary code) on a second job. Because the M code assumes it’s your only income, using it on two simultaneous jobs applies the tax-free/low-rate thresholds twice — under-taxing you all year and creating a real bill at year-end once IRD combines both incomes in your automatic assessment.

Worked Example — Two Jobs, One Student Loan

Meera has a student loan and works two jobs simultaneously: her main job pays $45,000/year, and a weekend retail job pays $12,000/year — a combined total of $57,000.

Job	Income	Correct code
Main job ($45,000)	Highest-paying, primary employment	M SL
Second job ($12,000)	Secondary employment; combined total income ($57,000) falls in the $53,501–$78,100 band	SH SL

Why not SB SL or S SL for the second job? Because secondary code selection is based on combined income across all jobs ($57,000), not the $12,000 that job alone pays — a distinction that trips up a lot of people who assume a smaller second job automatically means a lower-tier secondary code.

See your exact combined take-home pay across both jobs, with student loan repayments factored in, using free PAYE Calculator.

What Happens If You Get the SL Suffix Wrong?

Mistake	Consequence
Forgetting to add SL entirely	Student loan repayments aren’t deducted — you’ll owe a lump sum when IRD’s automatic assessment catches up
Using M SL on a second job	Under-taxed on that income, plus missed student loan repayments — compounds into a larger year-end bill
Not filing an IR330 at all	Your employer must deduct at the 45% “no-notification” rate — well above almost anyone’s real tax liability, refunded only after you file
Not updating your code after a pay rise crosses a threshold	Your secondary code may need to move up a band (e.g., S SL → SH SL) — check this any time your combined income shifts materially

How to Fix or Update Your Tax Code

Complete a new IR330 “Tax code declaration” form and give it to your employer (or to Work and Income, if the income is a benefit, NZ Super, or a Veteran’s Pension) — never to IRD directly. Your employer must apply the updated code from your next pay period after receiving it.

Frequently Asked Questions